This invention relates to improvements in drug delivery devices and particularly those for dispensing a metered dose of a medicament.
In metered dose inhalers, an aerosol stream from a pressurised dispensing container is fired towards a patient or user of the inhaler into an air flow. The air flow is created by a user inhaling through a mouthpiece of the inhaler and the medicament is released into this air flow at a point between the air inlet holes and the mouthpiece.
Conventional metering valves for use with pressurised dispensing containers comprise a valve stem coaxially slidable within a valve member defining an annular metering chamber, and outer and inner annular seals operative between the respective outer and inner ends of the valve stem and the valve member to seal the metering chamber therebetween. The valve stem is hollow whereby in a non-dispensing position of the valve stem, the metering chamber is connected to the container and charged with product therefrom. The valve stem is movable against the action of a spring to a dispensing position wherein the metering chamber is isolated from the container and vented to atmosphere for the discharge of product.
Other drug delivery devices include apparatus in which capsules containing a powdered medicament are mechanically opened at a dispensing station where inhaled air subsequently entrains the powder, which is then dispensed through a mouthpiece.
A problem with all such drug delivery devices is that deposition of the medicament, or a solid component from a suspension of a particulate product in a liquid propellant, on the internal surfaces and other components of the devices occurs after a number of operation cycles and/or storage. This can lead to reduced efficiency of operation of the device and of the resulting treatment in that deposition of the product reduces the amount of active drug available to be dispensed.
Some prior art devices rely on the dispenser being shaken in an attempt to dislodge the deposited particles as a result of the movement of a liquid propellant and product mixture. However, whilst this remedy is effective within the body of the container itself, it is not effective for particles deposited on the inner surfaces of the metering chamber. As the size of the chamber is significantly smaller, the restricted flow of fluid in the metering chamber (caused by the tortuosity of the flow path through the chamber) means that the fluid in the metering chamber does not move with enough energy to adequately remove the deposited particles.
One solution is proposed in our pending application GB 9721684.0 in which a liner of a material such as fluoropolymer, ceramic or glass is included to line a portion of the wall of a metering chamber in a metering valve. Although this solves the problem of deposition in these types of dispensers, it does require the re-design or modification of mouldings and mould tools for producing the valve members to allow for the insertion of the liner.
FR 2 756 502 describes an aerosol container wherein a paralene coating is applied to the spray pattern block. WO 95/15777 describes an injection device having container having a coating of polyparaxylelene on its inner surface. FR 2 740 527 describes a metering valve common in the art.
It is an object of the present invention to provide drug delivery devices in general in which the deposition of the product and active drug component is minimised.
According to the invention there is provided apparatus for dispensing a medicament comprising a housing adapted to receive a container or capsule for storing the medicament, a mouthpiece and duct means connecting an outlet of the container or capsule with the mouthpiece, characterised in that at least a portion of one or more of the internal surfaces of the duct and/or mouthpiece has a layer of a poly-para-xylylene polymer also known as Parylyne bonded thereto so as to reduce deposition of the medicament on said surfaces.